The invention relates to a pivot mounting assembly comprising a pivot arm for mounting a load in a vertically adjustable manner, said pivot arm being hinged to a pivot base to be pivotable about a horizontal axis. In particular, the pivot mounting assembly is suitable to be used in stands to mount, for example, lamps, visual display units and other devices, such as surgical microscopes which are to be provided vertically adjustable.
FIGS. 1a and 1b schematically show a conventional pivot mounting assembly comprising a pivot base 3 and a pivot arm 5 for mounting a load in vertically adjustable manner, here for example, a surgical microscope 7, in a position in which the pivot arm is raised (FIG. 1a) and in a position in which the pivot arm is lowered (FIG. 1b). One end of the pivot arm 5 is hinged to the pivot base 3 to be pivotable about a horizontal axis 9, and the other end supports the surgical microscope 7.
An auxiliary arm 11 is coupled parallel to the pivot arm 5 such that a vertical alignment of the surgical microscope 7 is maintained independent of the pivot position of the pivot arm 5.
The weight of the surgical microscope imparts a torque on the pivot arm about the pivot axis 9 which is largely compensated for by a force-providing device 13 in the form of a gas pressure spring, so that, if the frictional forces provided in the hinges of the pivot mounting assembly are sufficiently strong, the pivot arm largely remains in pivot positions adjusted by a user. For this purpose, one operative end 15 of the gas spring 13 is hinged to the pivot arm 5 in an area remote from the pivot axis 9, and the other operative end 17 of the gas pressure spring 13 is hinged to the pivot base 3 vertically spaced apart from the pivot axis 9. The compressive force of the gas spring imparts an antitorque moment on the pivot arm to compensate for the weight of the load 7.
However, as regards the compensation of the weight of the load independent of the pivot position, it has been found that the action of the force-providing device 13 in a lower pivot position is too strong, so that the pivot arm moves automatically upward in a direction indicated by an arrow 19 in FIG. 1b, and that the action of the force-providing device in an upper pivot position is too little, so that the arm automatically moves downward in a direction indicated by an arrow 21 in FIG. 1a. In order to prevent such automatic movement, usually the frictional forces in the hinges are increased which, however, impairs a smooth and precise adjustment of a desired pivot position by the user.
As to a solution of this problem, EP 0 433 426 A1 discloses a pivot mounting assembly, wherein the operative end of the force-providing device on the pivot base side is not hinged to the pivot base at a fixed location, but engages with a pin into an elongated, vertically extending hole provided in the pivot base, so that a vertical distance between a location where the force-providing device is supported on the pivot base and the horizontal axis is adjustable. The elongated hole has a specific curved configuration in order for the vertical distance between the support location and the horizontal axis to automatically change dependent on the pivot position of the pivot arm to thereby achieve an adjustment of the torque provided by the force-providing device dependent on the pivot position. However, it has been found in this respect that the movement of the operative end of the force-providing device on the pivot base side in the elongated hole dependent on the pivot position of the pivot arm is not precise enough, so that with reduced frictional forces, a compensation of the weight of the load independent of the pivot position is not adequately achieved.
In some embodiments, the invention provides a pivot mounting assembly which is adjustable with more ease.
In some embodiments, the invention provides a pivot mounting assembly of the above-described kind which enables a compensation of the weight of the load to be supported largely independent of the pivot position.
In some embodiments, the invention provides a pivot mounting assembly comprising a pivot arm for mounting a load in vertically adjustable manner, said pivot arm being hinged to a pivot base to be pivotable about a horizontal axis. In order to provide an antitorque moment to at least partially compensate for the torque imparted by the load on the pivot arm, a force-providing device, such as a coil pressure spring or a gas pressure spring, is provided, one operative end of which is hinged to the pivot arm spaced apart from the horizontal axis and the other operative end is supported on the pivot base vertically spaced apart from the horizontal axis. In this respect, a support location of the operative end of the force-providing device on the pivot base side is provided vertically adjustable on the pivot base in that a support surface extending transverse to the horizontal direction is provided on the pivot base, the support location of the force-providing device being shiftable along said support surface. The support surface is oriented such that, when the pivot arm is raised, the support location is moved downward, and, when the pivot arm is lowered, the support location is moved upward, in order for the antitorque moment to be adjusted dependent on the pivot position such that automatic movements of the pivot arm in its raised position or lowered position are suppressed.
According to embodiments of the invention, a second force-providing device is provided for producing a counterforce in at least a partial area of the support surface in order to prevent a downward or/and upward shift of the support location.
This counterforce provided by the second force-providing device allows a continuous and well-defined shift of the support location along the support surface at least in said partial area of the support surface dependent on the pivot position, and thus enables a compensation of the weight of the load to be held which is largely independent of the pivot position of the pivot arm and thus nearly flawless.
In some embodiments, the second force-providing device is a double-acting force-providing device which is configured such that it acts to hold the support location in a center of a shift area provided on the support surface for the support location, the second force-providing device preferably providing a counterforce which increases as the support location is shifted further from the center. To this end, the second force-providing device may comprise a spring assembly preferably comprising at least a pressure spring or a tension spring.
In some embodiments, the pivot mounting assembly is provided such that it is capable of compensating for loads of different magnitude. For this purpose, there is provided a drive which moves the shift area as such in which the support location is shiftable along the support surface in vertical direction relative to the horizontal axis. If the shift area as such is vertically spaced apart from the horizontal axis by a larger distance below the same, the pivot mounting assembly can compensate for larger loads than if the shift area is positioned closer to the horizontal axis.
With a given range in which the antitorque moment or the load to be compensated for is adjustable, the forces provided by the first force-providing device and the second force-providing device are preferably adjusted to each other such that the maximum counterforce of the second force-providing device is higher than the deflection force acting on the operative end of the force-providing device on the pivot base side due to the slope of the support surface for shifting the support location along the support surface. As a result, the current support location is well-defined by an equilibrium of the spring forces which results into a maximum compensation of the load weight independent of the pivot position. Preferably, this force adjustment is fulfilled for a partial area of the shift area and, particularly preferred, for the entire shift area. Moreover, this force adjustment is fulfilled at least for small adjustable antitorque moments and, particularly preferred, for all adjustable antitorque moments.
In some embodiments, a pair of end stops is further provided for a component of the operative end of the force-providing device on the pivot base side for delimiting the shift area as partial area of the support surface. In this respect, it is preferred that for the pair of end stops to be shiftable by the drive in vertical direction. The component of the end of the force-providing device on the pivot base side preferably contacts one of the end stops if the counterforce of the second force-providing device is insufficient to compensate for the deflection force caused by the slope of the support surface.
In some embodiments, the drive for shifting the shift area and the second force-providing device are functionally connected in series. In this respect, it is preferred that, in drive direction, one of the two operative ends of the drive is fixedly coupled to the end of the first force-providing device supported on the pivot base and the other operative end is hinged to the pivot base, with the second force-providing device being interposed. Alternatively, it is preferred that one of the two operative ends of the drive is hinged to the pivot base and the other operative end is coupled to the end of the first force-providing device supported on the pivot base, with the second force-providing device being interposed.
In one aspect, an embodiment of the end stops is obtained if at least one of the two end stops is provided by a pressure spring of the second force-providing device which embodies the end stop if it is completely compressed.
Moreover, in some embodiments, the drive may be a spindle drive, the spindle of which passes through coil springs of the second force-providing device in longitudinal direction thereof.
According to another embodiment of the pivot mounting device, the support area is provided on a carriage which is vertically shiftable in respect of the horizontal axis by means of the drive.
As to the geometric configuration of the support surface, shapes are preferred wherein a normal to the support surface slopes upward.